Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$244.26	8.734%	$265.5937	$265.59	$265.60	$265.60
Purchase #2	$78.47	9.140%	$85.6422	$85.64	$85.65	$85.60
Purchase #3	$67.95	6.843%	$72.5998	$72.60	$72.60	$72.60
Purchase #4	$16.69	3.319%	$17.2439	$17.24	$17.25	$17.20
Purchase #5	$50.58	12.436%	$56.8701	$56.87	$56.85	$56.90
Purchase #6	$141.83	10.283%	$156.4144	$156.41	$156.40	$156.40
Purchase #7	$20.40	6.516%	$21.7293	$21.73	$21.75	$21.70
7 purchase totals =	$620.18		$676.0934	$676.08	$676.10	$676.00